1. Field of the Invention
The invention relates generally to air mass flow sensors and more particularly to a multiple path air mass flow sensor having improved measurement accuracy.
2. Description of the Prior Art
Modern internal combustion engines typically intended for use in passenger vehicles and trucks include extensive use of operational sensors and microprocessors to control engine operation, improve performance and fuel economy, and reduce emissions. In fact, the great improvements in these often conflicting operational parameters of the last several decades would simply not have been possible without the use of these systems.
One of the most commonly used sensors with an internal combustion engine and electronic controller is an air mass flow sensor. Typically, an air mass flow sensor includes a resistance element which is located in an air intake duct, often immediately after the air filter and before the duct is subdivided into the branches of the intake manifold or other structure. So disposed, the air mass flow sensor is exposed to the instantaneous flow of air to the engine. Data from the sensor is utilized by the engine controller to compute the instantaneous air mass flow which is utilized to, for example, adjust the air fuel mixture and optimize engine performance in accordance with predetermined parameters.
Ideally the air mass flow sensor will be located in an intake duct to ensure that the air impinging upon it is representative of the total air flow so that the output of the sensor accurately reflects the total instantaneous air mass flowing through the duct. This can be a challenge because the often convoluted duct and varying air velocities may create complex flow patterns which render accurate flow measurement difficult. This problem is especially acute at low flow rates which represent the most critical engine operating condition from the standpoints of emissions and fuel economy. Although reducing the size of the intake duct would seem to be a solution to this problem, since the size of the intake duct is mandated by the air flow requirements of the engine at full load, reducing its size at the sensor location to improve measurement accuracy reduces the volume of air provided to the engine, increases flow resistance and will thus interfere with achieving maximum engine power output. A larger intake duct, however, reduces the flow velocity and, as noted, renders air mass flow measurement more difficult, particularly under low flow conditions—precisely those conditions that are most critical to optimum engine operation.
The foregoing discussion suggests that improvements in the design of mass air flow sensor assemblies is desirable.